Western Range Expansion of the Black Sandshell Mussel in Montana

Abstract

Newly discovered populations of the black sandshell mussel (Ligumia recta) from the Missouri and Marias Rivers in east-central Montana extend the species known range to its farthest western point in the United States and North America (west of 110° longitude).  The black sandshell is an introduced mussel in Montana and has become common and abundant in the Missouri River drainage since its establishment in Fort Peck Reservoir in the 1940’s.  Despite the increased distribution of the black sandshell westward across the prairie rivers of Montana, elsewhere in their native range, the species is declining.  This is a species of conservation concern in 21 states.  Habitat conditions and host fish abundances that are allowing this species to thrive in Montana’s rivers might provide valuable information for the conservation needs of this species in native states where it is now in decline.